1. Field of the Invention
This invention relates broadly to prostheses. More particularly, this invention relates to prostheses for the middle ear for replacement, in whole or in part, of one or more ossicles.
2. State of the Art
Hearing is facilitated by the tympanic membrane transforming sound in the form of acoustic sound waves within the outer ear into mechanical vibrations through the chain of ossicular bones (malleus, incus, stapes) in the middle ear. These vibrations are transmitted through the ossicular bones to the footplate of the stapes where micro or macro motion of this structure results in compression waves within the fluid of the inner ear. These compression waves lead to vibrations of the cilia (hair cells) located within the cochlear where they are translated into nerve impulses. The nerve impulses are sent to the brain via the cochlear nerve and are interpreted in the brain as sound.
Hearing efficiency can be lost to erosion of the ossicular bones. Various combinations or portions of the bones can be replaced. For example, the malleus and incus can be replaced leaving all or a portion of the stapes intact or the incus and stapes can be replaced leaving all or a portion of the malleus intact. Such a procedure is a partial ossicular replacement prosthesis, or PORP. Alternatively, the incus, malleus and stapes can be completely replaced by a prosthesis in a procedure referred to as a total ossicular replacement prosthesis, or TORP.
In addition, for implantation of certain middle ear transducer hearing devices, a majority of the long process (long arm) of the incus is removed during the procedure. If explantation of the hearing device is later required, it is necessary to reattach the incus to the stapes. Current incudo-stapedial joint (ISJ) prostheses may not have sufficient length to effectively span the gap between the remaining incus and the stapes capitulum.
Further, most incudo-stapedial joint prostheses, whether implanted due to erosion or post-explantation reconstructions, are designed with claws that are difficult to orient, require crimping, and may lead to delayed pressure necrosis of the ossicles to which it is attached. Other incudo-stapedial joint prostheses that require positioning of the prosthesis between the eroded incus and stapes capitulum are often unstable and are only effective for reconstructing small gaps between the eroded incus and stapes. Incudo-stapedial reconstruction using autograft bone chips or cartilage tend to deteriorate over time. The result is reoccurrence of ossicular discontinuity and decreased hearing.